I can confirm Maxime's solution works on my Asus FX73V which uses the Elan 1200 touchpad. I'm using gentoo with kernel 4.17.2, with all the relevant config options enabled (I2C, HID, ELAN, etc). I had 'acpi_osi=!' as a kernel parameter. Once I removed it the touchpad started working.
I can confirm Maxime's solution works on my Asus FX73V which uses the Elan 1200 touchpad. I'm using gentoo with kernel 4.17.2, with all the relevant config options enabled (I2C, HID, ELAN, etc). I had 'acpi_osi=!' as a kernel parameter. Once I removed it the touchpad started working.
Thanks Maxime!
Cristian